(1) Field of the Invention
The present invention relates to a method and an apparatus for extruding ceramic bodies with excellent dimensional accuracy.
(2) Related Art Statement
In order to extrude ceramic bodies, there has formerly been used a laterally extruding method in which the ceramic bodies are horizontally extruded. Since the extruded bodies are expediently set in the succeeding steps in the case of the laterally extruding method, this method is functional and effective in view of the entire extruding steps.
For instance, small size ceramic honeycomb structural shaped bodies having a diameter of not more than about 150 mm or a height of not more than about 150 mm when being horizontally extruded have a great cell density with a wall pitch of from 1 to 3 mm, and are light in weight. Thus, they will not deform by their self weight. Accordingly, they can horizontally be extruded.
However, if the above conventional laterally extruding technique is employed for ceramic components, such as ceramic rotors for pressure wave type superchargers, which have a relatively heavy weight and a smaller cell density, the extruded bodies deform due to their self weight until they are extruded from a die in a given length. Consequently, ceramic extruded products having excellent dimensional accuracy could not be obtained.
Also, since the self weight of large size ceramic honeycomb structural bodies having a diameter of more than 150 mm or a height of more than 150 mm when being horizontally extruded exceed their strength in the case of the lateral extruding, the extruded bodies deform due to their self weight so that products having excellent dimensional accuracy cannot be obtained.
On the other hand, there is also known a method of extruding ceramic bodies in an upward direction. In this upward extruding method, bending of extruded bodies is corrected by hands during extrusion, and the extruded bodies are taken out by using a jig. Thus roundness is outside a range of .+-.1.0 mm and a bending amount is 1.0 mm or more (Here, the roundness means a larger value between measured differences from the maximum diameter to the minimum diameter at each of opposite end faces in the case of an extruded body having a round section and the bending amount does the maximum distance l between a dried body 20 having a length of 150 mm and a base plate 21 placing the body 20 thereon as shown in FIG. 7).